The scientist, He Jiankui, used the gene-editing tool CRISPR-cas9, which is considered risky because it can inadvertently change a large portion of a person's DNA and have unintended consequences.

He, who worked on the experiment with US scientist Michael Deem, said he edited a gene called CCR5. The gene forms a "doorway" that allows HIV to enter cells, and turning it off makes people resistant to being infected in the future.

Even if everything went according to plan, the babies could be at greater risk of future health problems. The Associated Press reported that people without a regular CCR5 gene are more likely to catch the West Nile virus and die from the flu.

Since November, He has became the subject of several investigations. Last week, several news outlets reported that he has been detained and may face the death penalty, though the scientist has reportedly said he is fine.

Take a look at this timeline explaining the controversy surrounding He's research.

On November 26, He told an organizer of an international genome editing conference that he had altered the DNA of two baby girls. The Chinese scientist claimed he had altered the embryos for seven different couples, though only one person was pregnant as of November.

He Jiankui is reflected in a glass panel as he works at a computer at a laboratory in Shenzhen in southern China's Guangdong province.Mark Schiefelbein/AP Photo

He said his goal was not to cure an inherited disease or even to prevent one. Instead, he wanted the babies to have a specific trait: the ability to resist an HIV infection.

His claims had not been corroborated by other experts or published in a journal before the scientist came forward.

The university he worked at called for an investigation into He's research and said his work "seriously violated academic ethics and standards."

It was not immediately clear if the participants had known what He wanted to do. The Associated Press reported that consent forms called his project an "AIDS vaccine development" program.

He described his research at the Second International Summit on Human Genome Editing on November 28 in Hong Kong. He said he felt "proud" and noted that a third gene-edited baby could be born as a result of his work.

Scientist He Jiankui attends the International Summit on Human Genome Editing at the University of Hong Kong in Hong Kong, China, on November 28, 2018.
China Stringer Network/Reuters

He also said he submitted his research to a scientific journal for review, but he did not specify which publication he reached out to.

Southern University of Science and Technology of China in Shenzhen, where He conducted research, released a statement saying He's experiment was done "outside of the campus and was not reported to the University nor the Department."

Rice University, where Deem is listed as a professor of bioengineering, told STAT that it opened an investigation into the experiment.

China said on November 29 that it had suspended He's work, adding that his behavior seemed to violate Chinese law.

The audience reacts as He Jiankui, a Chinese researcher, speaks during the Human Genome Editing Conference in Hong Kong, on November 28, 2018.
Kin Cheung/AP

China's vice minister of science and technology, Xu Nanping, said He was still under investigation, but news reports had made it seem like he violated laws and broke "the bottom line of morality and ethics that the academic community adheres to," The New York Times reported.

He was initially supposed to speak again at the Second International Summit on Human Genome Editing, but his November 29 talk was canceled.

Robin Lovell-Badge — a British scientist who helped organize the summit — said He had chosen not to attend after learning that it would have been tough to find enough security for the event, The Times reported.

Lovell-Badge told The Times he did not regret allowing He to present his research at the summit, but giving him a second chance to speak may have been perceived as showing support.

The university denied on December 3 that it had detained He, but the scientist was not seen in public for about a month after the summit.

In this October 9, 2018, photo, Zhou Xiaoqin, left, and Qin Jinzhou, an embryologist who were part of the team working with scientist He Jiankui, view a time lapse image of embryos on a computer screen at a lab in Shenzhen in southern China's Guandong province.
Mark Schiefelbein/AP

He was spotted on the balcony of a university guesthouse in Shenzhen on December 26. Two days later, The New York Times reported that about a dozen guards were standing outside the apartment.

In this October 9, 2018 photo, an embryo receives a small dose of Cas9 protein and PCSK9 sgRNA in a sperm injection microscope in a laboratory in Shenzhen in southern China's Guangdong province.
Associated Press

It was the first sighting of He since the conference in Hong Kong.

He has been living in a fourth-floor apartment at the guesthouse, which is located on the Southern University of Science and Technology campus, The Times reported.

The scientist could be seen speaking with a woman who was carrying a baby, according to The Times. She appeared to be his wife.

Hotel staff confirmed to The Times that He was staying in the apartment, but The Times did not know if the guards had an affiliation with police or university officials. They did not identify themselves.

Chen Peng, a co-founder of the gene-testing company Vienomics, told The Times that he had spoken to He after the summit.

"He is safe," Chen told The Times. "But I don't know his exact whereabouts or what state he is in."

On January 7, The Telegraph reported that He could face the death penalty. A Beijing-based lawyer, however, says this is very unlikely.

He Jiankui, a Chinese researcher, speaks during the Human Genome Editing Conference in Hong Kong, on November 28, 2018.
Kin Cheung/AP

According to The Telegraph, Lovell-Badge and other British scientists said He could be charged with corruption and bribery, which can lead to the death penalty in China. He also seemed to break legally binding guidelines that prohibit scientists from implanting genetically altered embryos into humans, The Telegraph reported.

"He could be had up on all sorts of charges of corruption and being guilty of corruption in China these days is not something you want to be," Lovell-Badge told The Telegraph. "Quite a few people have lost their heads for corruption."

Two days later, STAT reported that He has been communicating with Lovell-Badge and another scientist who attended the summit. He has read Western news reports about himself and said he is doing well, downplaying claims that he is under house arrest and facing the death penalty.

A screen shows information of genomic data while He Jiankui, a Chinese researcher, speaking during the Human Genome Editing Conference in Hong Kong, on November 28, 2018.
Kin Cheung/AP

He told William Hurlbut, a neuroscientist and bioethicist at Stanford University, that he moved into the guesthouse "by mutual agreement," STAT reported.

The Chinese scientist said he is able to leave the guesthouse when he wants, adding that he has walked outside and visited the building's gym.

"He didn't convey to me that he finds the guards a constraining force at all, but instead feels they are protecting him," Hurlbut said, adding that He was concerned about threatening emails he had gotten in response to his experiment.

The scientist has reportedly received death threats since speaking at the summit.

STAT also reported that He has exchanged emails with Lovell-Badge, the summit organizer who works as a scientist at the Francis Crick Institute in London. He reportedly told Lovell-Badge that scientists who say his experiment would make the babies more likely to die from the flu are drawing conclusions from ambiguous research.

Lovell-Badge has also walked back some of his recent comments about He. In an interview with BCC, Lovell-Badge indicated he had been speculating about the death penalty possibility.

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